In a Multiprotocol Label Switching (MPLS) Ethernet virtual private network (EVPN), data centers are interconnected by means of an MPLS provider core network. Each data center may include devices that use the Multiprotocol-Border Gateway Protocol (MP-BGP) to dynamically communicate with each other.
BGP MPLS based EVPN is capable of supporting virtual machine (VM) mobility across data centers. As VMs move across data centers, traffic should be routed to those VMs along optimal paths, rather than taking sub-optimal detours. One technique for routing optimization involves injecting host routes of moved VMs into the wide area network (WAN) BGP to prevent traffic tromboning, in which the traffic flows first to the original data center from which the VM departed and only then to the new data center at which the VM landed. Injecting such host-level information into the WAN can result in a number of problems. For example, scalability issues arise as the number of moved VMs increases, which causes more information to be injected into the WAN, as well as an explosion of states in the data centers as the set of host route information maintained in the data centers increases. In addition, third party networks between the data centers may refuse to accept such a fine level of granularity in the host routes. That is, third party networks between the data centers may not accept routes smaller than a certain size, which would rule out such host routes.